Recent attentions have focused on a powder molding method, whereby a powder made from a soft magnetic material (hereinafter, referred to as a soft magnetic material powder) mixed with a resin is compression-molded, and is then heat-treated (i.e., curing method). The soft magnetic material powder can, for example, be made from an iron powder of a high degree of purity. Moreover, particles of the soft magnetic material powder can be coated with insulating films on surfaces thereof. As a resin to be mixed in the soft magnetic material powder, it is preferable that the resin possesses properties such as a behavior as a binder and for insulating at gaps of the soft magnetic material powder particles. A soft magnetic material powder compact molded as described above is employed for a motor core having a rotor and a stator.
More specifically, recent attentions have focused on some of the benefits which can be obtained, with high contribution, from the powder molding method: (1) expanding a possibility of shape design, downsizing a molded component (i.e., a compact), and cost reduction in manufacturing a compact; (2) improving a material yield ratio, and cost reduction in manufacturing a compact; (3) a simple process and cost reduction in manufacturing a compact; and (4) improving a material recycling efficiency so that an environment and resource can be conserved.
On the other hand, considerations should be given to points which should be improved about the powder molding method: (1) difficulty in assuring mechanical strength of a compact, especially at a high temperature atmosphere; (2) special design applied to a die, the special design which can facilitate a compact, to be taken out, or, to be ejected from the die; and (3) a magnetic property being inferior to the one of a pure iron plate.
In order to improve the aforementioned points of the powder molding method, JP2003-183702A discloses that a mixture of a polyamide based resin with a lubricating property, a polyphenylene sulfide resin (PPS) with a high melting point, and a soft magnetic material powder can contribute, at a high temperature atmosphere such as 200 degrees Celsius, to improvement of strength of a compact made from the mixture. However, recent requirements have led to a compact, which can possess a high degree of strength at a higher temperature atmosphere.
JP2002-329626A discloses, in order to enhance strength and a magnetic property of a compact, a method of applying a lubricant, such as a lithium stearate, at an interior of a die, thereby enabling to mold a compact with a material not including resin material. However, in this method, a process of applying a lubricant at an interior of a die is essentially required. In such circumstances, it has been found that there is a danger of lowering productivity of a compact, and of undesirably increasing a molding cost, especially when a lubricant is required to a complicatedly shaped die. Accordingly, the method of applying a lubricant at an interior of a die disclosed herein may not be readily applied to industrial uses.
JP2002-280209A discloses a technology, whereby a compact is made from a mixture of a thermosetting resin, a lubricant and an iron, the compact can possess, in favor of a thermosetting resin, a sufficient degree of mechanical strength at a high-temperature atmosphere, and, in favor of a lubricant, a sufficient degree of lubricating property. However, it has been found that a remaining lubricant may become a source of corruption of the compact, and moreover the remaining lubricant may permeate outside.
The present invention has been made in view of the above circumstances, and provides a soft magnetic powder material, which can be readily molded, can assure a high degree of strength of a compact at a high temperature atmosphere, and is excellent at a magnetic property. Moreover, the present invention provides a method of manufacturing a soft magnetic powder compact made from the aforementioned soft magnetic powder material.